Navigation Links
Nervous system


The nervous system of an animal coordinates the activity of the muscles, monitors the organs, constructs and processes input from the senses, and initiates actions. (see Central Nervous System).

In animals with brains, the nervous system also generates and conducts thoughts and emotions. Thus it is the system that animates "animals" (sponges are an exception). Chemicals that target the activity of nerves generally are the most rapidly acting toxins, typically causing paralysis and/or death.

Contents

Anatomy

The nervous system consists basically of two types of cells:

  • Neurons are the primary cells of the nervous system
  • Glia are secondary cells involved in nourishment and structural support.

Rapid signalling within the nervous system occurs by two primary mechanisms:

Vertebrate nervous systems

The nervous systems of vertebrate animals are often divided into a central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS consists of all other nerves and neurons that do not lie within the CNS. The large majority of what are commonly called nerves (which are actually axonal processes of nerve cells) are considered to be PNS. The peripheral nervous system can also be roughly seen as consisting of sensory pathways and motor pathways , the latter being divided into the somatic (voluntary) nervous system and the autonomic nervous system.

The somatic nervous system is the voluntary part of the nervous system that coordinates a body's movements, such as maintaining a particular posture and walking. The autonomic nervous system is the involuntary part of the nervous system where all of the internal maintenance is taken care of.

The autonomic nervous system is then divided into the sympathetic division and parasympathetic division. The sympathetic nervous system responds to impending danger or stress, and is responsible for the increase of one's heartbeat and blood pressure, among other physiological changes, along with the sense of excitement he feels. The parasympathetic nervous system, on the other hand, is evident when a person is resting and feels relaxed, and is responsible for such things as the constriction of the pupil, the slowing of the heart, the dilation of the blood vessels, and the stimulation of the digestive and geniturinary systems.

Nervous system diversity

The nervous system varies greatly among living animals. Cnidarians, such as sea anemones and jellyfish, have a nerve net, in which the activation of any one neuron triggers a wave of activation across the entire network. These waves are both afferent and efferent, representing both the sensation of chemicals or touch as well as the stimulus of the animals' reflexive mechanical response.The worms and flukes of the phylum platyhelminthes possess a network of nerves that operates like a more conventional nervous system, but lack a brain. Annelid worms and tunicates have a primitive brain called a ganglionic mass, which is a bundle of several nerves. Based in part on commonalities in embryonic development among all chordates, the tunicate brain is believed to resemble the evolutionary precursor of the vertebrate brainstem.

See also


'"/>


(Date:7/2/2020)... ... July 01, 2020 , ... ... 1a findings of Neihulizumab, a biologic for the treatment of steroid-refractory acute graft-versus-host ... by hemato-oncologist Dr. Paul J Martin of the Fred Hutchinson Cancer Research Center, ...
(Date:7/1/2020)... ... July 01, 2020 , ... ... completed the purchase of Teva-Takeda Pharmaceuticals’ packaging facility in Minakuchi, located in the ... clinical supply facility located in Kakegawa, the new 60,000-square-foot facility will provide customers ...
(Date:6/28/2020)... ... June 25, 2020 , ... Genedata, ... that it has entered into a multi-year contract with Merus N.V., a ... translational and clinical research strategy to discover and develop ground-breaking drugs. The ...
Breaking Biology News(10 mins):
Other biology definition